面试手写第五期

一. 实现一个函数用来对 URL 的 querystring 进行编码

const data = {a: 3,b: 4,c: 5,
};
function stringify(data) {const pairs = Object.entries(data);const qs = pairs.map(([k, v]) => {let noValue = false;if (v === null || v === undefined || typeof v === "object") {noValue = true;}return `${encodeURIComponent(k)}=${noValue ? "" : encodeURIComponent(v)}`;}).join("&");return qs;
}
// 对 data 编码后得到 querystring 如下
//=> 'a=3&b=4&c=5'
stringify(data);

二. 如何实现一个数组洗牌函数 shuffle

function shuffle(array) {let len = array.length;let _array = [...array];while (len) {let index = Math.floor(Math.random() * len--);[_array[index], _array[len]] = [_array[len], _array[index]];}return _array;
}

三. 异步加法的几种方式

串行

function add(a, b) {return Promise.resolve(a + b);
}
async function sum(arr) {let s = arr[0];for (let i = 1; i < arr.length; i++) {s = await add(s, arr[i]);}return s;
}

并行

function add(a, b) {return Promise.resolve(a + b);
}function chunk(list, size) {const l = [];for (let i = 0; i < list.length; i++) {const index = Math.floor(i / size);l[index] ??= [];l[index].push(list[i]);}return l;
}async function sum(arr) {if (arr.length === 1) return arr[0];const promises = chunk(arr, 2).map(([x, y]) =>// 注意此时单数的情况y === undefined ? x : add(x, y),);return Promise.all(promises).then((list) => sum(list));
}sum([1, 2, 3, 4]).then(res => {console.log(res);
})

四. 实现trim函数

function trim(str = "") {str = String(str);let left = 0;let right = str.length - 1;while (/\s/.test(str[left]) && left < right) {left += 1;}while (/\s/.test(str[right]) && left < right) {right -= 1;}return str.slice(left, right + 1);
}

五. 求多个数组的交集

function intersection(...args) {return args.reduce((res, cur) => [...new Set(res.filter(item => cur.includes(item)))])
}
console.log(intersection([1, 2, 2], [1, 2, 2], [1, 2]));

六. 手写实现render函数

function get(source, path, defaultValue = undefined) {// a[3].b -> a.3.b -> [a, 3, b]const paths = path.replace(/\[(\w+)\]/g, ".$1").replace(/\["(\w+)"\]/g, ".$1").replace(/\['(\w+)'\]/g, ".$1").split(".");let result = source;for (const p of paths) {result = result?.[p];}return result === undefined ? defaultValue : result;
}function render(template, data) {return template.replace(/{{\s+([^\s]+)\s+}}/g, (capture, key) => {return get(data, key);});
}

七. 驼峰转- -转驼峰

//驼峰转短横线
function toKebabCase(str) {let res = str.replace(/([A-Z])/g, (all, i) => {return "-" + i.toLowerCase();});if (res.slice(0, 1) === "-") {res = res.slice(1); //去除开头的-}return res;
}
//短横线转驼峰
function toCamelCase(str) {return str.replace(/-([a-zA-Z])/g, function (all, i) {return i.toUpperCase();});
}console.log(toCamelCase("get-element-by-id"));
console.log(toKebabCase("GetElementById"));

八. instanceof实现

function fakeInstanceOf(instance, parent) {if (typeof instance !== "object" && typeof instance !== "function") {return false;}let proto = instance?.__proto__ || null;while (true) {if (proto === null) {return false;}if (proto === parent.prototype) {return true;}proto = proto.__proto__;}
}//=> true
console.log(fakeInstanceOf([], Array));//=> true
console.log(fakeInstanceOf([], Object));//=> true
console.log(fakeInstanceOf(x => x, Object));//=> false
console.log(fakeInstanceOf('hello', Object));

九. 组合问题

function combinationGenerator(m, n) {const results = [];function backtracking(start, currentComb) {if (currentComb.length === n) {results.push(currentComb.slice());return;}for (let i = start; i <= m; i++) {currentComb.push(i);backtracking(i + 1, currentComb);currentComb.pop();}}backtracking(1, []);return results;
}
console.log(combinationGenerator(3, 2));

十. 字符串分组

function groupAnagrams(strs) {const groups = new Map();for (let str of strs) {const sortStr = str.split('').sort().join();if (!groups.has(sortStr)) {groups.set(sortStr, []);}groups.get(sortStr).push(str);}return Array.from(groups.values());
}const strings = ['eat', 'tea', 'tan', 'ate', 'nat', 'bat'];
console.log(groupAnagrams(strings));